Friday the 13th Part V: A New Beginning(1985) [Demon]: Stabbed in the back with a spear by Dick Wieand, through the outhouse wall. (Thanks to Wen)

The Return of the Living Dead (1985) [Spider]: Killed in an explosion (along with everybody else in the movie) when the military drops a nuclear bomb on the city in an attempt to destroy all the zombies. (Thanks to Wen)

Life(1999) [Biscuit]: Shot in the back by guards when he suicidally attempts to escape, rather than face life outside prison. (Thanks to Venice)

The Adventures of Pluto Nash(2002) [Miguel]: Killed in an explosion when Club Pluto blows up. (Thanks to Tommy)